1. Field of the Invention
The present invention relates to an artificial oil lift system and more specifically, to a linear motor automatic control circuit assembly for controlling the operation of a 3-phase linear motor-driven submersible oil pump of an artificial oil lift system.
2. Description of the Related Art
Beam/sucker-rod pumping is the most popular artificial lift in oil well for the production of crude oil today. A beam/sucker-rod pumping system has a submersible oil pump set in the oil well, and a rotary motor mounted on the ground to cause the walking beam to pivot up and down. The walking beam causes the sucker rod string attached to opposite end of the walking beam to rise and fall. This activates the submersible oil pump which lifts the oil up to the ground surface. The speed of the submersible oil pump that is installed in an oil well is adjustable by the worker at the ground. Further, the depth of the oil level in an oil well may change subject to the geological structure and the status of flowing of fluid into the oil well. Conventionally, the control of pump speed of a submersible oil pump in an oil well is done subject to the submergence depth of the submersible oil pump, and the measurement of the depth of the oil level is done externally with a independent acoustic echo device. When adjusting the pump speed of a submersible oil pump in an oil well, the whole artificial lift system must be stopped. Further, the adjustment of the pump speed is complicated and limited to discrete stroke number adjustment. A continuous pump speed adjustment is not workable.
U.S. Pat. No. 731,627 discloses an oil pumping unit using a submersible oil pump driven by a synchronizing three-phase linear motor. According to this design, the oil pumping unit uses a synchronizing linear motor to reciprocate a pump, causing the pump to lift the oil from the oil well to the ground continuously during the down stroke as well as during the up stroke.